Regional blood flow distributions in organs of experimental animals can be measured effectively by combining fluorescent microsphere methods with imaging cryomicrotomy. The number of flow measurements that can be made in a single animal is currently limited because using different colors of fluorescent microspheres for each measurement fills the available spectral range. The research proposed here will develop nanocrystal-coded microspheres that will emit fluorescence at only two narrow wavelength ranges, but whose relative intensities can be used to classify microspheres based on simple ratiometric intensity coding. Feasibility will be demonstrated during Phase I using a designed set of seven nanocrystal- coded microspheres that will be used in studies of phantoms, perfused rat hearts, and interorgan blood flow distribution in live animals. Measurements of regional flow using fluorescent-polystyrene microspheres and nanocrystals-coded microspheres in perfused hearts will be correlated to establish validity of the coded microsphere method. Use of coded microspheres to measure regional blood flow will free spectral space for concurrent measurements using labeled antibodies, lectins, fluorescent proteins, and structural stains. Successful implementation of this research will result in new products and services for measuring regional blood flow. [unreadable] [unreadable] [unreadable]